US2054299A - Hydroxy cellulose ether solutions - Google Patents

Description

Patented Sept. 15, 1936 UNITED STATES PATENT OFFICE George A. Richter, Berlin, N. H., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application 31, 1934, Serial No. 728,301

Claims. '(01. 106-40) This invention relates to the preparation of hydroxy cellulose ether solutions such as are used in makingartificial silk filaments, transparent films, and other ultimate products. Solu- 5 tions of this kind are prepared by dissolving the solid hydroxy'cellulose ether in caustic soda solution. In producing the ultimate product, the ether solution is brought in contact with suitable acidic media, such as a sulphuric acid solution of sodium sulphate, which function to precipitate or regenerate the ether in solid condition from the solution. Thus, the ether solution may be extruded through spinnerets into acid-setting baths which serve to regenerate the ether in the form of filaments or threads. In making filaments, transparent films, or similar manufactures, it is necessary that the ether solution be sufiiciently fluent to lend itself to the desired extruding, spreading, or similar operation and that such fluency exist when the solution contains sufficient ether dissolved therein to yield upon Setting or precipitation an ultimate manufacture possessed of suflicient body or ether substance. This means, of course, that the ether solution must be stable in the sense that it will not gel or coagulate before it is put through the spinning, spreading, or similar operation.

In working with hydroxy cellulose ether solutions, I haveobserved that they are apt to vary greatly in stability, depending upon such factors as the kind of cellulose employed as raw mate rial, the amount of etherifying agent with which etherification is effected, the conditions of etherification, and the after-treatment which the ether undergoes preparatory to being dissolved in caustic soda solution. I have further observed that the stability of'the cellulose ether solution affords no criterion of the quality of the filaments, films, or other products derived from such solution.

40 Indeed, I have found that the filaments and films produced from ether solutions of low stability often possess distinctly greater wet strength than those produced from solutions of high stability. This is possibly attributable to the fact that the cellulose ether regenerated from a solution of high stability has a greater tendency to reassume a dissolved state when wetted with water. High stability is also frequently associated with very fluid solutions that are made from ethers which, in turn, are produced from highly depolymerized cellulose.

In accordance with the present invention,'I prepare a solution of hydroxy cellulose ether that represents a blend of an ether of high solution stability and an ether of low solution stability,

for I have discovered that such a solution partakes of the stability ,quality of the ether of high solution stability but yields filaments, films, and similar products of higher wet strength than those obtainable from a solution of the ether of 5 high solution stability alone. Thus, by preparing a solution of hydroxy cellulose ether that represents a blend of approximately equal proportions of an ether of high solution stability, for instance, an ether displaying practically no gelling 10 or coagulating tendencies in solution even after the solution has been allowed to stand for days, and an ether of low solution stability, for instance, an ether displaying decided gelling or coagulating tendencies in solution immediately or 15 after the solution has been allowed to stand only for a few hours, I have found it possible practically to do away with the instability of the ether of low solution stability, for the solution representing such a blend can stand for days without 20 gelling or coagulating, partaking of the stability of a solution of the ether of high solution stability alone. In other words, the solution representing such a blend does not possess, as might be expected, a stability constituting an average or 25 arithmetic mean of the stability values of the component ethers, but acquires a vastly greater stability. Apparently, the effect of the ether of high solution stability is that of a peptizing or stabilizing agent, acting to peptize or stabilize to 30 a decided degree the solution of ether of low solution stability without, however, itself being materially impaired in its solution stability. The netresult is, as already indicated, a stable ether solution whose component of low solution sta- 35 bility imparts higher wet strength to the ultimate product derived from the solution.

Another important advantage to be gained by my invention is that I am enabled to prepare a solution representing a blend of ethers such as 40 hereinbefore described at a lower expense than a solution containing only ether of high solution stability. The fact is that whereas hydroxy cellulose ethersof high solution stability are usually realized only when special treatment is per- 45 formed on the cellulose fiber used as raw material and/or on the resulting ether and/or when etherification is carried out under special conditions, no such special treatment or special conditions of etherification are necessary in arriv- 50 ing at ethers of low solution stability. Thus, ethers of high solution stability may be prepared to advantage from cellulose fiber that has undergone a mercerizing and/or other chemical treatment that lowers the solution viscosity 55 of the fiber. They may be produced'by hydrolyzing ethers of comparatively high solution viscosity under heat and pressure in dilute solutions of mineral acids, such as hydrochloric and S111- phuric acid, which act to reduce greatly the solution viscosity of such ethers. They may result; also from'the use of a comparatively large fore, it becomes'advantageous to prepare asolution of hydroxy cellulose ether that represents 'a' blend of ethers'produced froin both mercerized and unin'ercerized cellulose fiber; a blend of 'ethers produced from both cellulose fibenof high solution viscosity and cellulose fiber of lowsolua tion viscosityg and a blendof ether of high solu-- .tion viscosity and an ether of low solution 'viscosity. I Irideed,i.'it: becomes advantageous. ,to.

originates'from such mixed sourcesv as cotton, softwood, hardwood, -etc., since fibers or pulps of such different, origins may yield. hydroxy cellue prepare a solution of hydroxy cellulose ether that representsa blend of others whose cellulose base lose ethers. of widely varying solution stability.

.In arriving at the hydroxy cellulose ether solution ofthe present invention, various practices may be adopted. 'For instance, I may blendtwo. or more cellulose. fibers. of, different character:

' .istics, etherify the blend, and then dissolve the resulting 1 product in caustic soda solution to produce a stableether solution. Thus, a blend of-unmercerized' and'mercerized cellulose'fibers may be etherified and then dissolved in caustic soda solution. If desired, each kindof fiber maybe etherified independently andthe resulting 'ethers.

' blended'preparatory to being dissolved in caustic.

soda solutionf'Or the same kindof fiber may be etherified .in difierent, batches with different proportions of etherifying agent to produce.

ethers differing. sharply in their solution sta.-.-

bility, whereupon the others. may be blended and dissolved in jcaustic soda. solution. 7 Where the blending takes place before etherification or after etherification, it is. preferably done before the step; of dissolving the ethers. In other words, I

prefer not to dissolve. each of the others independently and then. mixthe resulting solutions of, 'difierent' stabilities, but'to blend the solid 'etherspreparatory to. putting them into. solution.

In any eventhowever, the caustic; soda, solution. in which an ether or blend of others is, to be dis,-:

solved is preferably first, frozen in admixture with the ether or ethers and then thawed out under vigorous mixing orkneading actiomas this 7 tends to activate. the ether or .blend of ethers ior=1cornplete solution, that is, witha minimum oi residual undissolved matter that-detracts from the clarity'of the solution.

j A specific. example of procedureaccordant with my invention may be substantially as follows. Mercerized cellulose of lo'wsolution viscosity is etherified with ethylene oxide in the amount of 1 about 15 or more, based on the weight of the cellulose, to produce-- a hydroxy ethyl ether of cellulose Which -afte r activation, goes readily into solution fand fyie'ldsa highly stable ether Solu i n. amehn nat atd ot en t el or coagulateeven after a week or more of stand- Unmercerized elluloseof highsolution viscosityiis. etherified'with, say, only about 6%. of

ethyleneogridafbased on the weight of cellulose,

to produce a hydroxy ethyl ether of cellulose, which even after activation, does not go into solution readily and yields a highly unstable ether solution, namely, one that tends to gel or coagulate immediately or after standing only for a few hours or a shorter period of time. When such ethers .are blended in the proportion of, say, 50% each, and the blend is activated for solution by mixing with the caustic soda solution in which solution is to be effected, freezing the solution, and thawing out the solution under vigorous. stirring or kneading action, the blend than that of a. solution produced from only the ether of low solutionstability. Indeed, the solution of the blendihas a stability that approximatesthat of a solution produced from only the ethro-f high solution stability, remaining stable even after a Week or more of standing. Besides imparting high stability to the solution. of. the blend, the ethercomponent of high solution stability. reduces greatly the. viscosity of the $0111? 'tion of the blend. It, isrdesirable that the solution produced,- from'theblend contain dissolved therein bout. 7% of caustic soda and about 8% .ofcellulose ether, s such a sol tion not only possesses the desired stability, but also. the workable fluidity and cellulose ether concentration for making'su-ch products. as. filaments and films. Such a solution may also be. used in impregnating paper, felts, orwoven fabrics, in which latter connection, however, it may, if desired, be. readily diluted with water to any desired concentration.

The present inventionincludes; blends of more than two hydroxy cellulose ethers of different stabil-ities dissolved stably in caustic soda solution, such blendscomprising an ether of high; solution stability and an ether of low solution stability, forinstance, a hydroxy ethyl etherhi h c and a hyd o rethyl. ethe of; lowethyl content, hereinbefore described. In any blend prepared in accordance, with myinvention, the ether of high solution stability has; a solution stability sufiiciently high and is present n suflicient amount, to preserve the solution of the blend against gelling or coagulating after standing for at least, a few days, even though a solution of only the ether of low solution stability gels or-coagulates upon standing for only a few hours-or even a shorter period ft mo:

I i o ten he s that a. el u s ether aving low solution stability will gel as it is being put into solution without, first producing a fluent olut on S d s-r of tab it is apt t st n t e as f: o he s r duc m u marcerized cellulose or iiroin mercerized cellulose oflow solution viscosity; For instance, when hydroxy cellulose others: so produced are admixed with caustic soda. solution, the solution then frozen, and themixture mascerated while it, is being thawed out, the resulting solution, is often a clear, substantially fiberless, rubber-dike gel. Inother words, the resulting solution is in workable into filaments, films, or other manu 30 to 35 C., during this period. As already indicated, I prefer not to dissolve the ether of low solution stability independently of the ether of high solution stability with which blending is to be effected, but to blend the two ethers preparatory to putting them both into solution,

thereby avoiding the production of a gelled solution of the ether of low solution stability.

I claim:-

I. A process of stabilizing a caustic soda solution of hydroxy cellulose ether tending to gel after standing at most for a few hours, which comprises dissolving in such solution substantially at the time of its preparation a substantial amount of another hydroxy cellulose ether tending by itself to remain ungelled in solution for a markedly longer period of time so as to impart to the solution of mixed ethers a stability against gelling much greater than the arithmetic mean of the stabilities against gelling of both said ethers, thereby greatly increasing the solution stability of said first-named ether of low solution stability.

2. A process of stabilizing a caustic soda solution of hydroxy cellulose ether tending to gel after standing at most for a few hours, which comprises dissolving in such solution substantially at the time of its preparation a substantial amount of another hydroxy cellulose ether tending by itself to remain ungelled in solution for at least a few days so as to impart to the solution of mixed ethers a stability against gelling much greater than the arithmetic mean of the stabilities against gelling of both said ethers, thereby greatly increasing the solution stability of said first-named ether of low solution stability.

3. A process of stabilizing a caustic soda solution of hydroxy cellulose ether tending to gel after standing at most for a few hours, which comprises dissolving in such solution substantially at the time of its preparation a substantial amount of another hydroxy cellulose ether tending by itself to remain ungelled in solution for at least a few days so as to impart to the solution of mixed ethers a stability against gelling much greater than the arithmetic mean of the stabilities against gelling of both said ethers, said second-named ether of high solution stability being dissolved in amount suflicient to preserve the solution of mixed ethers against gelling for at least a few days.

4. A process of stabilizing a caustic soda solution of hydroxy ethyl ether of cellulose tending to gel after standing at most for a few hours, which comprises dissolving in such solution substantially at the time of its preparation a substantial amount of another hydroxy ethyl ether of cellulose of higher ethyl content tending by itself to remain ungelled in solution for a markedly longer period of time so as to impart to the solution of mixed ethers a stability against gelling much greater than the arithmetic mean of the stability against gelling of both said ethers, thereby greatly increasing the solution stability of said first-named ether of lower ethyl content and lower solution stability.

5. A process of stabilizing a caustic soda solution of hydroxy ethyl ether of an unmercerized cellulose tending to gel after standing at most for a few hours, which comprises dissolving in such solution substantially at the time of its preparation a substantial amount of another hydroxy ethyl ether of a mercerized cellulose tending by itself to remain in ungelled solution for a markedly longer period of time so as to impart to the solution of mixed ethers a stability against gelling much greater than the arithmetic mean of the stability against gelling of both said ethers, thereby greatly increasing the solution stability of said first-named ether of unmercerized cellulose and low solution stability.

GEORGE A. RICHTER.